1. Field of the Invention
This invention relates to draglines and more particularly, to a pair of tightline apparatus for mounting on the fairleads of the dragline in the path of the drag ropes, respectively, to facilitate termination of dragline operation in the event that the dragline bucket approaches the dragline boom past a predetermined close proximity. Each tightline apparatus includes a U-shaped engaging bar pivoted to a fairlead swivel frame of the dragline, such that the engaging bar is located above and in transverse alignment with one of the drag ropes extending from the upper vertical sheaves of the fairlead swivel frame to the bucket. In a preferred embodiment each engaging bar is spring-loaded in this position, such that movement of the drag ropes upwardly responsive to swinging of the dragline bucket inwardly toward the boom past a predetermined safety point causes the drag ropes to engage the respective engaging bars, pivot the engaging bars against the spring bias and activate a pair of limit switches, also mounted on the fairlead swivel frame. This action locks the brakes on the drag and hoist drum of the dragline and prevents dangerously close approach of the bucket to the dragline boom.
2. Description of the Prior Art
One of the problems which is inherent in the operation of draglines is that of inadvertently causing the dragline bucket to approach the boom past a predetermined distance, thereby placing dangerous stress on the boom. In some instances, dragline booms have been known to collapse under the stress created when the bucket is swung into critical close proximity to the boom, at great expense and extreme hazard to the workers. Accordingly, the dragline operator must exercise great care in pulling the bucket toward the dragline responsive to tension placed on the drag ropes, to insure that the bucket does not encroach on this predetermined critical distance from the boom. This distance may be inadvertently encroached upon under circumstances where the operator is not careful or where he is incapacitated by an accident such as a heart attack, stroke or other eventuality. Accordingly, there exists a need in the art for a device that will automatically terminate operation of the dragline under circumstances where this critical distance between the dragline bucket and boom is encroached upon.
It is an object of this invention to provide a tightline apparatus for mounting on a dragline and automatically terminating operation of the dragline under circumstances where the dragline bucket encroaches on a preselected critical distance with respect to the boom.
Another object of this invention is to provide at least one tightline apparatus which is designed to mount on the fairlead swivel frame of a dragline in alignment with at least one of the drag ropes for engagement with the drag rope under circumstances where the bucket is maneuvered within a predetermined critical distance from the dragline boom.
Yet another object of this invention is to provide a pair of new and improved tightline apparatus, each of which is characterized by an engaging bar pivotally mounted on a fairlead swivel frame of the dragline above and in transverse alignment with one of the drag ropes and a limit switch provided in each tightline apparatus in alignment with the corresponding engaging bar, such that upward movement of the drag ropes responsive to swinging of the dragline bucket into a predetermined unsafe distance between the dragline bucket and the boom causes the drag ropes to engage the corresponding engaging bars and pivot the engaging bars, thereby energizing the limit switches and locking the brakes on the drag and hoist drums of the dragline.